In regulated power supplies of the series switching transistor type difficulties have arisen in that the base drive current to the series switching transistor has been found to vary with change in ambient temperature, with the drive current decreasing at lower temperatures and increasing at higher temperatures. This characteristic is opposite to that desired since the series switching transistor requires greater drive current at lower temperatures and less drive current at higher temperatures. In low temperature environments the base drive current could decrease to a level that would not allow the power supply to operate and at elevated temperatures the base drive current could increase to a point where damage to the series switching transistor could occur.